Among cathode active materials for lithium secondary batteries, a lithium cobalt oxide having a layered structure, such as LiCoO2, is the most commonly used cathode material. Lithium cobalt oxide has a problem in that Co is very expensive and toxic, and also has a problem in that it has poor structural stability caused by phase transformation due to lithium deintercalation during charging.
To solve these problems, LiNixCoyMnzO2 (x+y+z=1) having a reduced content of Co and including Ni, Co, and Mn has been proposed, and NCM523 has been used for a commercial purpose. Here, N, C and M of the “NCM523” refer to Ni, Co, and Mn, respectively, and 523 refers to contents of Ni, Co, and Mn, respectively. That is, “NCM523” refers to “LiNi0.5Co0.2Mn0.3O2.”
Recently, materials such as NCM622 in which the content of Ni exceeds 50% have been commercialized due to a current demand for higher energy density, but have a limitation of realizing a high energy density required for electric cars by manufacturers.